This reaction corresponding to the equation CO+H2O→CO2+H2 is among the most important reactions in the chemical industry. Now, this reaction has also gained interest for power stations using fossil fuels. The background to this is the present trend toward low-CO2 combustion in the firing of these power stations. In the precombustion approach, the carbon monoxide has to be converted into carbon dioxide according to the abovementioned equation (1) before combustion in order to be able to separate off the entire carbon in the form of carbon dioxide. In this way, the energy of the carbon monoxide is transferred (shifted) to hydrogen which can be used in the gas turbines. However, for the removal of the products carbon dioxide and also hydrogen, separation from the gas phase is highly energy-consuming.
In the approaches customary to date, the carbon monoxide shift reaction and the removal of the carbon dioxide are carried out in essential separate substeps. Firstly, the carbon monoxide shift reaction is carried out in the gas phase. The carbon dioxide is then separated off in a further process step. A typical example of the removal is the Rectisol scrub in which the carbon dioxide is absorbed in cooled methanol. Appropriately low temperatures are necessary here in order to separate off the carbon dioxide, and a great amount of energy is necessary for cooling, which reduces the overall efficiency of the power station.
The European patent EP 0 299 995 B1 describes a process for carrying out the carbon monoxide shift reaction, with this proceeding in the liquid phase. At the same time, removal of the carbon dioxide formed can be realized. This applies particularly to example 6 of the patent document and also to FIG. 2. Here, water-containing methanol is used as solvent. The pH of the methanol is increased by addition of a carbonate, for example potassium carbonate. However, there are two important points in this patent document which make use appear questionable: it is not ensured that the gaseous starting material carbon monoxide (CO) can be converted significantly quickly into the liquid phase for industrial use in order then to be converted into formate. Furthermore, a significant loss of hydrogen in the carbon dioxide stream separated off has to be expected because of the relatively high solubility in the solvent used.